Method of preparing acrylonitrile/ethylene copolymers



United States Patent M 3,227,697 METHOD OF PREPARING ACRYLONITRILE/ETHYLENE COPOLYMERS Melford R. Eeamon, Indianapolis, Ind., and CharlesR.

Donaldson, Tuscola, Ill., assignors to National Distillers and ChemicalCorporation, New York, N.Y., a corporation of Virginia N0 Drawing. FiledMar. 8, 1963, Ser. No. 263,716 9 Claims. (Cl. 260-855) This inventionrelates to the manufacture of copolymers of ethylene and is particularlyconcerned with copolymers of ethylene with acrylonitrile. Still moreparticularly it relates to the manufacture of copolymers of ethylene andacrylonitrile that are especially suited for use in general packagingoperations.

In manufacturing films from ethylene polymers, especially films that areto be converted into bags for foodstuffs (fresh produce, candy, nuts,poultry, meat, etc.), soft goods, pharmaceutical and surgical supplies,hardware, toys, and the like, it is important that the film producthave, among other characteristics, outstanding mechanicalpropertiesjthat is, the film must be tough and flexible in order towithstand mechanical shocks and stresses to packages assembledtherefrom. It is desirable also that the resin from which the film isproduced should have good processing properties, such as, for example,high drawdown rate and heat sealability.

It is known that ethylene can be polymerized with a wide variety ofcomonomers. In general, however, special synthesis conditions or processequipment have been required to make such copolymers.

It is an object of this invention to overcome the disadvantages of theprior art processes for producing copolmers of ethylene.

It is another object of the invention to provide a process whereby apolyethylene copolymer product can be obtained using the apparatus andtechniques already in commercial practice for large-scale production ofpolyethylene.

Another object of the invention is to provide a combination ofreactants, reaction conditions, and reaction-influencing substances thatgives results in a high pressure process that are quite difierent fromresults previously achieved in high pressure polymerization.

Additional objects and advantages will become apparent from thefollowing detailed description.

It has now been found that a resin product having a novel combination ofproperties that makes it particularly attractive for use in molding orin manufacturing films can be prepared by subjecting ethylene inadmixture with a small amount, for example between about 0.1 weightpercent and about 1.0 weight percent, based on ethylene, ofacrylonitrile as a comonomer to selected polymerization conditions ofelevated temperature and elevated pressure in the presence of a suitablecatalyst and, if desired, a suitable catalyst carrier.

The resulting copolymer has a density of about 0.918 to about 0.925, amelt index in the range of about 1.0 to about 10.0, and, in addition,good processing and mechanical properties. The copolymer may beconverted into a product that has increased haze, drawndown, and

3,227,697 Patented Jan. 4-, 1956 stress crack resistance; decreasedstrength; and decreased stiffness.

The copolymers produced in accordance with this invention have thusacquired improved mechanical properties without detrimental efiFect ontheir other physical properties that make them particularly applicablefor use in molding and in film extrusion. For example, the product is aneasily-handled, good-working resin. Since the flow characteristics ofthe resin are excellent, high-impact film may be produced from it athigh production rates. When conventional additives are used, the filmhas excellent printability; it can be handled without difiiculty onautomatic bag-making and packaging machinery; and bags made from thesefilms stack without blocking, fill easily, and seal readily andsecurely. Suitable additives are compounds such as, for example,saturated amides for control of slip and blocking behavior.

The amount of comonomer used can vary from about 0.1 up to about 1.0weight percent, based on the ethylene feed; preferably about 0.15 up toabout 0.3 weight percent is used.

The catalyst selected for the process of this invention can be anyethylene copolymerization catalyst suitable for use under the reactionconditions embodied herein. Particularly suitable are t-butylperpivalate, t-butyl perzenzoate, dilauroyl peroxide, t-butylperacetate, t-butyl peroxide, and other compounds of comparable freeradical activity, and mixtures thereof. The amount of catalyst employedcan vary over a wide range of from about 0.001 up to about 5 Weightpercent, based on the ethylene feed. The catalyst can be used alone orit can be used in the presence of a catalyst carrier, that is, an inertliquid solvent or diluent such as, for example, benzene, hydrocarbonoils such as mineral oils, kerosenes, saturated hydrocarbons, and thelike, and mixtures thereof. The amount of catalyst carrier can rangefrom about 0 up to about 100 percent by weight, based on the catalystsolution, and it is preferably used in an amount of from about to 99percent.

As set forth above, the process in accordance with the present inventionis carried out at conditions used in the high pressure polymerization ofethylene to prepare high molecular weight polymers. In general, theethylene admixed with the comonomer is compressed by multi-stagecompressors up to the operating pressure in the polymeri bation reactor.The catalyst with or without a catalyst carrier and with otheradditives, if desired, such as, for example, up to about 5.0 weightpercent, based on the catalyst carrier, of an antioxidant, are injectedinto the ethylene feed line. In the polymerization reactor the ethyleneand the comonomer are polymerized to form a solid or semi-solidcopolymer under pressures within the range of about 17,000 to about30,000 pounds per square inch, and preferably about 20,000 to about25,000 p.s.i., and at temperatures within the range of about 300 to 500F., and preferably about 350 to 450 F. The product copolymer and theunreacted gas are then passed through pressure let-down valuves into gasseparators, which may be one or more in series. The unreacted gas isseparated and recycled, if desired, to the ethylene feed line. Thecopolymer product remaining in the final gas separator is extruded,cooled to room temperature, and subjected to conventionalafter-treatment steps, such as chopping, shredding, reprocessing,blending, Banburying, or the like.

' inventive method.

In order to get the preferred copolymer product, it is essential boththat the pressure be in the range of about 17,000 to 30,000 p.s.i. andthat the temperature be within the range of about 300 to 500 F. If thepressure is substantially below about 17,000 p.s.i. or substantiallyabove about 30,000 p.s.i. or substantially below about 300 F. orsubstantially above about 500 F., the resulting copolymer does not havethe desired combination of properties.

The relative ease with which this improved copolymerization process canbe carried out is an obvious advantage. As previously stated, there is nneed to employ special equipment or reaction techniques in practisingthe Single-stage or multi-stage processes can be utilized, and thecopolymerization can he carried out as a bulk polymerization or in thepresence of solvents,

such as benzene, or of dispersants, such as water. The pressure attainedcan be achieved as usual by pressuring the reactor t the desired degreewith ethylene. It will be understood that the usual polymer recoveryprocesses are applicable to the method of this invention; for example,

the unreacted ethylene and comonomer can be separated from the moltencopolymer in a vessel in which the tem perature is essentially that ofthe reaction and the pressure is reduced to about one tenth that of thereaction. The pressure of the copolymer can be further reduced to aboutto about p.s.i., and the molten copolymer can then be extruded, cooled,and pelletized.

The copolymer of this invention may be molded or converted to a film byany convenient procedure. The film may be blown, fiat, or cast. Filmsmay be formed in thicknesses ranging in gauge from about 0.5 mil,suitable for use as garment bags, up to about 10 mils, suitable for useas tarpaulins.

The copolymer of this invention may also be used to improve theproperties of waxes, such as petroleumderived waxes, eithermicrocrystalline or paraflin; synthetic waxes; and so forth. Suchcompositions are expected to have unique properties of toughness, scufiresistance, adhesive strength, ductility, gloss, low water vaportransmission, and processability. The amount of ethylene/acrylonitrilecopolymer blended with the wax may vary over a wide range so that suchcompositions are useful, for example, as coatings, e.g., for paper,cardboard, cloth, fiber, foil, plastics such as polyolefins, rugbackings, and the like; moldings, e.g., molded food containers,disposable containers, etc.; laminates, e.g., for adhering varioussubstrates together, as aluminum to cellophane, aluminum to polyolefinssuch as polypropylene; etc.

If desired, the copolymer of this invention may be used infinely-divided form, that is, where the copolymer has an average size ofless than about 10 mesh and preferably within the range of about 150 to2,000 microns. The finely-divided, or powdered, material may be used,for example, in dry form to coat articles by dip coating in either astatic or fluidized bed, by powder coating wherein 'the powder isapplied by spraying or dusting, and by flame spraying. In dispersedform, the powders may be applied as coatings by roller coating, spraycoating, slush coating, and dip coating to a variety of substrates. Thepowder also may be foamed and/ or used in powder molding techniques; asa paper pulp additive; a mold release agent for rubber; an additive towaxes, paints, or polishes; a binder for non-woven fabrics; and thelike. The finelydivided material may be prepared by mechanical grinding,by solution or dispersion techniques, or by any other convenient method.

The invention will be more fully understood by reference to thefollowing examples which are illustrative only and which are notintended to limit the scope of the invention except as indicated by theappended claims. Unless otherwise specified, all parts are given byweight.

The density of the product is determined, in gram/cc., by a hydrostaticmethod, that is, by weighing a sample of 4 the copolymer at 23 C., firstin air and then in kerosene (ASTM test method D792-60T).

Melt index describes the flow behavior of a product at a specifiedtemperature and under a specified pressure. It is here determined (ASTMtest method D123 8-57T) by measuring the flow rate, expressed ingrams/l0 minutes, on extrusion through an orifice 0.0825 inch indiameter by 0.315 inch long under a pressure of 43.1 p.s.i., at 190 C.

The yield strength is the tensile stress, in pounds per square inch ofcross-sectional area of the test specimen, at which the slope of astress-strain curve first becomes zero (ASTM test method D63 8-60T).

Torsional stifiness, measured in accordance with ASTM test methodDl043-5l, is the value obtained by measuring the angular deflectionoccurring when the specimen is subjected to an applied torque.

The heat softening point (Vicat softening temperature) is thetemperature at which the test specimen becomes too soft to withstandstresses and keep its shape. It is the temperature at which a fiat-endedneedle of 1 sq. mm. cross section under a load of -1 kg. penetrates 1mm. into a specimen. The temperature of the sample is increased at auniform rate (ASTM test method Dl525-58T).

Stress crack resistance is determined as follows (ASTM test methodDl693-60T): Bent specimens of the plastic having a controlledimperfection on one surface are exposed to the action of a surfaceactive agent. The proportion of the total number of specimens whichcrack in a given time is observed.

Flat film drawdown is determined as follows: a'web of film is extrudedat about 480 F. from a slot die set at 12 mils into a water quench bath.At constant output of grams per minute, the web is pulled away byuniformly accelerating nip rolls until it breaks. Drawdown is the linearspeed in feet per minute at which the web breaks.

EXAMPLE I (A) Ethylene admixed with 0.12 weight percent, based onethylene, of acrylonitrile as comonomer and 0.13 weight percent, basedon ethylene, of dilauroyl peroxide as catalyst were fed into aconventional autoclave reactor. The temperature inside of the reactorwas 378 F. and the reactor pressure was maintained at 20,000 pounds persquare inch. The conversion achieved was about 9.9 percent. A solidcopolymer was continuously produced.

Compression molded plaques for testing the mechanical properties of thecopolymer were made on an Atlas press at 300 F. The plaques were cutinto test specimens suitable for use on conventional instruments formeasurement of mechanical properties. Properties of the product aretabulated below.

Blown film (1.5 mils thick) of the copolymer was extruded at 325 F. on a2-inch Egan extruder with a 16:1 L:D ratio and a 25:1 blow-up ratio. Theextruder output was about 25 pounds per hour. Properties of the productare tabulated below.

(B) The procedure of Example I(A) was repeated except that no comonomerwas used. The properties of the comparative ethylene homopolymer aretabulated below.

EXAMPLE II (A) The procedure of Example I(A) was repeated except thatthe amount of acrylonitrile was 0.24 weight percent, the catalyst was0.008 weight percent of t-butyl perbenzoate, and the reactor temperaturewas 450 F. The conversion achieved was 9.3 percent. Results aretabulated below.

(B) The procedure of Example 11(A) was repeated except that no comonomerwas used. The properties of the ethylene homopolymer are tabulatedbelow.

Table Results of Example IA 13 HA IIB Density. 0. 922 0. 922 0. 918 0.918 Melt Index 1. 74 1. 7 4. 76 4. 76 Haze, percent 52. 4 23. 8 28. 416. 7 Gloss, percent 2. 6. 3 3. 1 7. 1 Transmittance, percent..- 0. 060. 65 0.2 2.7 Elmendorf Tear:

MD 1 76. 2 102. 6 47. 3 48. 0 TD 1 08.0 94. 5 76.0 57.0 Dart Drop,Grams. 82.5 83 116 98 Elongation, percent:

MD 286 350 293 290 TD 474 380 149 460 Tensile Strength, p.s.i.:

MD 2, 410 1, 020 2, 100 TD 2, 220 1, 1, 990 Yield Strength p 5 MD 1, 4401,060 1, 255 TD 1, 370 1, 560 980 1, 280 Modulus, p.s.i.:

3 D 21,800 24,100 14, 800 20,300 D 24, 100 Torsional Stifiness, psi 14,400 40, 000 20, 300 30, 000 Low Temperature Brittleness, C.

for F50 76 -76 -76 76 Stress Crack, hours for F50 48 0. 25 0.25 0. 44Vicat Softening Point, C 81. 0 99. 0 85.8 91. 5 Drawdown, 1p m 81 11059.0

1 MDMachine direction; TD-Transverse direction.

As can be seen from the tabulated data, the copolymers of ethylene andacrylonitrile in general have lower strength, stiffness, low temperaturebrittleness, and softening point than the comparative ethylenehomopolymers made under the same conditions.

While there are above disclosed but a limited number of embodiments ofthe process of the invention herein presented, it is possible to producestill other embodiments without departing from the inventive conceptherein disclosed.

What is claimed:

1. A process for copolymerizing ethylene and acrylonitrile whichcomprises reacting a mixture of ethylene and about 0.1 to about 1.0weight percent, based on the ethylene feed, of acryl-onitrile at atemperature between about 300 and 500 F. and a pressure of about 17,000to about 30,000 pounds per square inch in the presence of about 0.001 toabout 5 weight percent, based on the ethylene feed, of a free radicalcopolymerization catalyst in a stirred closed reaction zone.

2. The process of claim 1 wherein the temperature is between about 350and 450 F. and the pressure is between about 20,000 and 25,000 poundsper square inch.

3. A copolymer of ethylene and acrylonitrile prepared by the process ofclaim 1.

4. A shaped article produced by molding a copolymer of ethylene andacrylonitrile prepared by the process of claim 1.

5. A film prepared from a copolymer of ethylene and acrylonitrileprepared by the process of claim 1.

6. A process for copolymerization of ethylene and acrylonitrile whichcomprises reacting a mixture f ethylene and about 0.15 to about 0.3weight percent, based on the ethylene feed, of the acrylonitrile at atemperature between about 350 and 450 F. and a pressure between about20,000 and 25,000 pounds per square inch in the presence of about 0.001to about 5 weight percent, based on the ethylene feed, of a free radicalcopolymerization catalyst in a stirred closed reaction zone.

7. A copolymer of ethylene and acrylonitrile prepared by the process ofclaim 6.

8. A shaped article produced by molding a copolymer of ethylene andacrylonitrile prepared by the process of claim 6.

9. A film prepared from a copolymer of ethylene and acrylonitrileprepared by the process of claim '6.

References Cited by the Examiner UNITED STATES PATENTS 2,436,256 2/ l948Hanford et a1. 260 85.5 2,467,234 4/1949 Sargent et al. 260-85.52,650,913 9/1953 Boyd 260-85.5 3,119,803 1/1964 Horkowitz 260'86.7

OTHER REFERENCES Kresser: Polyethylene, Reinhold Publishing Corp.

JOSEPH L. SCHOFER, Primary Examiner.

DONALD E. CZAJA, Examiner.

H. WONG, Assistant Examiner.

1. A PROCESS FOR COMPOLYMERIZING ETHYLENE AND ACRYLONITRILE WHICHCOMPRISES REACTING A MIXTURE OF ETHYLENE AND ABOUT 0.1 TO ABOUT 1.0WEIGHT PERCENT, BASED ON THE ETHYLENE FEED, OF ACRYLONITRILE AT ATEMPERATURE BETWEEN ABOUT 300* AND 500*F. AND A PRESSURE OF ABOUT 17,000TO ABOUT 30,000 POUNDS PER SQUARE INCH IN THE PRESENCE OF ABOUT 0.001 TOABOUT 5 WEIGHT PERCENT, BASED ON THE ETHYLENE FEED, OF A FREE RADICALCOPOLYMERIZATION CATALYST IN A STIRRED CLOSED REACTION ZONE.